The present invention relates to development of latent electrostatic images, and more specifically, to electrode members for use in a developer unit in electrophotographic printing machines. Specifically, the present invention relates to electrode wires fabricated such that the phenomena known as wire history and wire contamination are minimized.
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the photoconductive member thereof. The uniformly charged portion of the photoconductive member is exposed to light corresponding to an original document being reproduced. The source of the light may be light reflected from an original document or light emanating from a laser. This records an electrostatic latent image on the photoconductive member.
After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed depositing developer material onto the latent electrostatic image. Two component and single component developer materials are commonly used for rendering the latent electrostatic images visible.
A typical two-component developer material comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single component developer material typically comprises toner particles such as silica and titanium and also contain debris picked up from the environment. Toner particles are attracted to the latent image forming a toner powder image on the photoconductive member. The toner powder image is subsequently transferred to a copy sheet. Finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
One type of development apparatus for developing latent images and comprising single component developer is known as a scavengless development system, one that uses a donor roll for transporting charged toner to a development zone. At least one, but preferably a plurality of electrode members is closely spaced to the donor roll in the development zone. An AC voltage is applied to the electrode members thereby forming a toner cloud in the development zone, area between the electrode members and the imaged surface. The electrostatic fields emanating from the latent images attract toner from the toner cloud thereby effecting development of the latent images.
Another type of development apparatus for developing latent images on a charge retentive surface such as a photoconductor comprises a two-component developer and is known as a Hybrid Scavengless Development (HSD) system that employs a magnetic brush developer roller for transporting carrier having toner adhering triboelectrically thereto. A donor roll is used in this configuration also to transport charged toner to the development zone. The donor roll and magnetic roller are electrically biased relative to one another. Toner is attracted to the donor roll from the magnetic roller. The electrically biased electrode members cause detachment of toner particles from the donor roll forming a toner powder cloud in the development zone, and the latent image attracts the toner particles thereto. In this way, the latent image recorded on the photoconductive member is rendered visible.
Various types of development systems have hereinbefore been used as illustrated by the following disclosures, which may be relevant to certain aspects of the present invention. In addition to possibly having some relevance to the question of patentability of the present invention, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 4,868,600 granted to Hays et al describes an apparatus wherein a donor roll transports toner to a region opposed from a surface on which a latent image is recorded. A plurality of electrode members are positioned in the space between the latent image surface and the donor roll and electrically biased to detach toner from the donor roll to form a toner cloud. Detached toner from the cloud develops the latent image.
U.S. Pat. No. 4,984,019 granted to Folkins discloses a developer unit having a donor roll with electrode members disposed adjacent thereto in a development zone. A magnetic roller transports developer material to the donor roll. Toner particles are attracted from the magnetic roller to the donor roller. When the developer unit is inactivated, the electrode members are vibrated to remove contaminants therefrom.
U.S. Pat. No. 5,124,749 granted to Bares discloses an apparatus in which a donor roll advances toner to an electrostatic latent image recorded on a photoconductive member wherein a plurality of electrode wires are positioned in the space between the donor roll and the photoconductive member. The wires are electrically biased to detach the toner from the donor roll so as to form a toner cloud in the space between the electrode wires and the photoconductive member. The powder cloud develops the latent image. A damping material is coated on a portion of the electrode wires at the position of attachment to the electrode supporting members for the purpose of damping vibration of the electrode wires.
U.S. Pat. Nos. 5,300,339 and 5,448,342 both granted to Hays et al., the subject matter of each which is hereby incorporated by reference in their entirety, disclose a coated toner transport roll containing a core with a coating thereover.
U.S. Pat. No. 5,172,170 granted to Hays et al discloses an apparatus in which a donor roll advances toner to an electrostatic latent image recorded on a photoconductive member. The donor roll includes a dielectric layer disposed about the circumferential surface of the roll between adjacent grooves.
U.S. Pat. No. 5,422,709 teaches an apparatus in which a donor roll advances toner to an electrostatic latent image recorded on a photoconductive member. A plurality of electrode wires is positioned in the space between the donor roll and the photoconductive member. The electrode wires extend in a transverse direction relative to the longitudinal axis of the donor roll. The electrode wires are electrically biased to detach the toner from the donor roll so as to form a toner cloud in the space between the electrode wires and photoconductive members. Detached toner from the toner cloud develops the latent image. Electrode wires contact a portion of the surface of the donor roll. As the donor roll rotates, friction between the electrode wires and donor roll causes trapped debris to move away from the toner powder cloud region so as to minimize contamination-produced streaks on the developed image.
U.S. Pat. No. 5,734,954 granted to Eklund et al discloses an apparatus for developing latent electrostatic images wherein a power supply controller, in communication with the power supply, is adapted to adjust an electrode member electrical biasing to avoid air breakdown induced contamination of the electrode member with toner.
U.S. Pat. No. 5,778,290 granted to Badesha et al discloses an apparatus and process for reducing accumulation of toner from the surface of an electrode member in a development unit of an electrostatographic printing apparatus by providing a composite coating on at least a portion of the electrode member.
U.S. Pat. No. 5,787,329 granted to Laing et al discloses an electrode member positioned in the space between the surface and the donor member, the electrode member being closely spaced from the donor member and being electrically biased to detach toner from the donor member thereby enabling the formation of a toner cloud in the space between the electrode member and the surface with detached toner from the toner cloud developing the latent image, wherein opposed end regions of the electrode member are attached to wire supports adapted to support the opposed end regions of said electrode member; and an organic coating on at least a portion of nonattached regions of said electrode member.
U.S. Pat. No. 5,805,964 granted to Badesha et al discloses an electrode member positioned in the space between the surface and the donor member, the electrode member being closely spaced from the donor member and being electrically biased to detach toner from the donor member thereby enabling the formation of a toner cloud in the space between the electrode member and the surface with detached toner from the toner cloud developing the latent image, wherein opposed end regions of the electrode member are attached to wire supports adapted to support the opposed end regions of said electrode member; and a low surface energy inorganic material coating on at least a portion of nonattached regions of said electrode member.
U.S. Pat. No. 5,999,781 granted to Gervasi et al on Dec. 7, 1999 discloses an apparatus and process for reducing accumulation of toner from the surface of an electrode member in a development unit of an electrostatographic printing apparatus by providing an composition coating including a polyimide or epoxy resin, an optional lubricant and metal compound selected from the group consisting of chromium (III) oxide, zinc oxide, cobalt oxide, nickel oxide, cupric oxide, cuprous oxide, chromium sulfate and cadmium sulfide on at least a portion of the electrode member.
U.S. Pat. No. 6,049,686 granted to Folkins et al discloses a developer unit for developing a latent image recorded on an image-receiving member with marking particles, to form a developed image. A donor member is spaced from the image receiving member and adapted to transport marking particles to a development zone adjacent the image-receiving member. An electrode is positioned in the development zone between the image receiving member and the donor member. A voltage supply is provided for electrically biasing the electrode during a developing operation with an alternating current bias to detach marking particles from the donor member, forming a cloud of marking particles in the development zone, and developing the latent image with marking particles from the cloud. The voltage supply periodically electrically biases the electrode during a cleaning operation with a direct current bias and with an alternating current bias so that toner is effectively removed from the wire. The bias levels are chosen to reduce field-induced redeposition of right or wrong sign toner.
As noted above, both Scavengless and Hybrid Scavengless Development (HSD) rely on electrically biased wires, disposed intermediate a developer transport such as a donor roll and a charge retentive surface such as a photoreceptor, to energize the toner into a cloud for development of the latent image on a photoreceptor.
When several images of contrasting (i.e. images varying between high and low values) throughput are developed on the charge retentive surface, toner in the low throughput areas remains on the wire from image to image resulting in a long resident time for the toner on the wires in these low throughput areas. This long resident time of toner moving across the wire without development allows discreet areas on top of the wire and toner to interact triboelectrically. The result is creation of a charge differential that allows toner to electrostatically attach to the wire and buildup in the areas of low throughput that results in a change in development resulting in images that contain underdeveloped areas. This change in development is known as wire history.
The problem of wire history has been satisfactorily solved by coating the wires with a polymeric material that precludes the formation of such a charge differential between the toner and the coated wire. However, polymeric coatings employed for solving the wire history problem are comparatively soft with respect to conventional xerographic developer additives such as titanium and silica. This hardness disparity between the wire coating and the developer additives allows the toner additives to become impacted in the polymer coating resulting in improper image development and/or deposition of toner in areas of the photoreceptor not intended for development. Wire impaction from toner additives takes place along the entire length of an electrode wire but occurs first at the inboard and outboard ends of the wire. The buildup of contaminants on the wire precludes proper image development. Since wire contamination takes place first at the inboard and outboard areas of the wires, underdevelopment is initially more severe adjacent these areas than toward the center of the wires. Additionally, over time, the contaminant buildup, which initially occurs on the bottom of the wire, works its way around to the top of the wire. Contaminants on top of the wire decrease the spacing between the photoconductive surface and the wire to a point where toner particles mixed with the contaminants actually contact the photoconductive surface thereby depositing toner particles in unintended areas. The change in development resulting from additive impaction on the wire coating is commonly referred to as wire contamination. Thus improper development occurs when contaminants are on the bottom of the wire and unintended development eventually occurs when the contaminants work their way around to the top of the wire.
This invention resulted from the need to provide wire electrodes for use in Scavengless development systems wherein both of the failure modes of wire history and wire contamination associated with Hybrid Scavengless Development (HSD) technology are minimized. To overcome the failure modes of both wire history and wire contamination, the general requirements are such that the wire must not produce a charge differential with the toner for wire history and must be hard and smooth so as to prevent wire contamination.
Pursuant to the intents and purposes of the present invention, development electrode wire material is treated using Ion Implantation so as to minimize the creation of charge potential between the electrode wires and developer material during frictional contact. Treatment of the wires using Ion Implantation for minimizing the creation of a charge potential is effected without diminishing the hardness of the wire material. In fact, wire hardness and resistance to wire contamination is enhanced using Ion Implantation for coating the wires. Ion Implantation is a low-temperature vacuum technology that uses a linear accelerator to create a beam of charged atoms, or ions. The ion beam is then shaped and directed toward the device surface such as an electrode wire, embedding ions into the material. The ions are accelerated to an electrode wire at energies high enough to bury them below the target""s surface and sub-surface. The ions become implanted in the substrate without altering the surface finish of the target yet alter the tribo-charging properties of the coated wire.
The use of Ion Implantation for implanting suitable materials into is a target component such as the electrode wires used for Hybrid Scavengless Development accommodates both requirements of reduced wire history and wire contamination. As noted above, Ion Implantation is a process where atoms of an element are converted to ions and accelerated to high speeds and directed towards the target substrate. By selecting the correct atoms to implant, the tribo-charging properties of the target can be tuned to be neutral with respect to the contacting developer material. Stated differently, the Electronegativity (EN) to be discussed below, of the wire is tuned to the EN of the developer material. By choosing a suitable metallic material for the wire substrate and implanting ions of select elements the wire history performance of the wire can approach that of polymer coated wires of the prior art while maintaining the desired hardness and surface finish to minimize wire contamination.
The concept of employing Ion Implantation to alter the tribo-charging properties of a substrate material departs from the typical use of the process. Normally ion implantation is used to alter the mechanical properties of a substrate such as hardness and wear resistance. A typical use of an ion beam implanter is to alter the near surface properties of semiconductor materials that are done without regard to matching Electronegativity values of interacting materials.
For a general understanding of the features of the present invention, a description thereof will be made with reference to the drawings.